[sheepdog] ledger object leak

[Valerio Pachera]

Hi, this isn't urgent but I opened a bug as a reminder:
https://bugs.launchpad.net/sheepdog-project/+bug/1384951

Correct me if I'm wrong: as a workaround, when there are no snapshots
I can safely remove all ledger objects but the last.

cd /mnt/sheep/0
ls 8*
807c2b2500000000
807c2b2700000000
807c2b2900000000
807c2b2a00000000
807c2b2b00000000
807c2b2c00000000
807c2b2e00000000
807c2b2f00000000

ls 8* | grep -v 807c2b2f00000000 | xargs rm

Thank you.